MU-Radar Recorded Field-Aligned Irregularities in the F2 Region and Associated Sporadic-E Disturbances.

Recordings by the MU-radar of two ionospheric events involving F2-layer field-aligned irregularities (FAIs) on one particular night in a sunspot-maximum period (July 24/25, 1991) have been examined and compared with ionospheric events deduced from the analyses of ionograms from the adjacent ionosonde stations of Akita and Kokubunji. Ionograms from three other Japanese stations have also been analysed. The analyses detected two medium-scale travelling ionospheric disturbances (MS-TIDs) which pass through the MU-radar observing region at times close to those of the FAI recordings. The MS-TIDs seem to be propagating at both F2-layer and Es layer levels. F2-layer macroscale changes and Es-layer enhancement (particularly the Es enhancements) have been used to track the disturbances over significant distances from Wakkanai in the north to Yamagawa in the south, and even to the island of Okinawa (located some 2, 500 km from Wakkanai). Spread-F is recorded during the passage of these MS-TIDs, but only at some stations. Quite apart from the apparent association of these MS-TIDs with the FAI recordings, these results would seem to reinforce other results which indicate an association between macroscale F2-layer height changes and enhanced sporadic-E occurrence.